High BP Injures Brain Even in Early Midlife

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An MRI study on third-generation participants in the Framingham Heart Study found evidence of structural brain abnormalities associated with higher systolic blood pressure even in early middle age.

Note that fractional anisotropy, which has been linked to cognitive decline in the elderly, was decreased in participants with higher systolic blood pressures and was also independently associated with increasing age.

Having high blood pressure in early middle age is already associated with structural changes in the brain -- changes similar to those seen in late life that are associated with poor brain health and loss of cognitive ability, researchers found.

On a composite measure of brain health, normotensive individuals whose average age was about 40 scored higher (β = 1.88, 95% CI 0.46 to 3.3) than those who were prehypertensive (β = 1.56, 95% CI 1.37 to 1.75, P<0.001), according to Charles DeCarli, MD, of the University of California Davis, and colleagues.

What this meant, they explained, was that the brain health of a 33-year-old hypertensive person was equivalent in age to that of a 40-year-old with normal blood pressure.

Previous research has revealed changes in the brain of older patients with hypertension, including atrophy of the gray matter, injury to the white matter, and silent infarcts.

Recent studies using sensitive MRI techniques have identified subtle hypertension-related damage to the white matter, before the characteristic areas of hyperintensity can be detected.

For instance, diffusion tensor imaging has shown alterations in fractional anisotropy in hypertensive individuals, suggesting the presence of damaged neural axons in the anterior corpus callosum.

In the elderly, fractional anisotropy changes in that area of the brain are associated with cognitive decline and dementia, the researchers noted.

Determining if these changes had already begun to appear in midlife would add the preservation of cognitive ability to the known cardiovascular benefits of blood pressure control, they observed.

To explore this, they performed brain MRI on 579 participants in the third-generation cohort of the Framingham Heart Study who ranged in age from 19 to 63.

The microstructural integrity of the white matter was assessed by measuring fractional anisotropy and mean diffusivity.

Gray matter volume and and white matter hyperintensities also were mapped, and total cranial volume was quantified in a voxel-based analysis. Principal component analysis was then used to compute the composite measure of brain integrity.

Increasing age and higher systolic blood pressure were both independently associated with a reduction of 6.5% in fractional anisotropy, not only in the anterior corpus callosum but also in the frontal-occipital fasciculi and in fibers extending to the superior frontal gyrus from the thalamus.

Age and blood pressure also were associated with decreases of approximately 9% in gray-matter volume, particularly in the temporal lobe and middle temporal gyrus.

Possible explanations for how blood pressure might influence brain microstructure include arterial stiffening and compromised blood flow, but complex mechanisms are likely to be involved and further studies will be needed to clarify this.

Limitations of the study included the homogeneous population in the Framingham Heart Study and the likelihood that healthier individuals are more likely to participate in studies such as this.

Nonetheless, there is an important public health message from this study: that blood pressure control needs to be "early and optimal," the investigators wrote. "Given current evidence that both the degree and duration of hypertension are associated with continuous adverse effects on late-life brain injury and cognition, early and aggressive treatment may be required to have significant public impact."

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